As a rule, propellant charges for cannons consist either of loose grains of flakes, rods or perforated cylinders, or of sticks with or without perforations enclosed in a case or cartridge, in which the length of the perforated propellant sticks has, for combustion reasons, hitherto been generally limited to a maximum of 100 times the diameter of the powder's inner-channels. Moreover, charges of this type are often composed of mixtures of different batches of two or more powders. In this context, it is of minor importance whether the powder is--from the purely chemical point of view of the single, double or varying triple-base type or whether or not the surface is coated or inhibited.
Hence, the present invention now relates to propellant charges for cannon ammunition which may be given an extremely high charge density and high progressivity, the invention also relating to a method of producing such charges.
Generally speaking, a normal propellant may be considered as having a specific gravity of approx 1.53. In charges consisting of propellant of loose grains or sticks of the above-mentioned types, a charge density of approx 0.9 g/cc will be attained. On the other hand, according to the present invention, it will be possible to produce charges with charge densities of up to 1.4 g/cc i.e a considerable increase. This may be of value in those cases where the strength parameters and performance of a cannon, for example a howitzer, a tank gun or a naval gun, enable the weapon to withstand larger propellant charges than could be accommodated in the chamber of the weapon if the powder were in the loose state or in sticks. Thus, the charge according to the present invention would make it possible to improve the performance of older high-quality artillery pieces.
According to the present invention propellant charges for cannons are proposed which consist of a number of tubular propellant sticks of large length in relation to the diameter of their combustion channels and partly of loosely disposed, disoriented grains, flakes or single- or multiperforated short tubes of propellant. According to the present invention this type of charge is made possible because the propellant sticks are provided with slits or incisions which connects the propellant sticks' burning channels with their outer surfaces.
The present invention can be described in more detail as propellant charges composed, in the first instance, of a bundle or a collection of linearly arranged bundles of densely packed stick propellant of a total length corresponding at least to the major fraction of the available combustion space, and in which each stick consists of a single- or multiperforated propellant stick which has been provided at predetermined distances throughout its entire length, with points of weakness in the form of cross-sectional slits, open grooves or bored holes which extend, from the outside of the propellant stick at least as far as its centre, or alternatively where every propellant stick is provided with longitudinal, continuous or intermittent slits from the outside of the stick into all of its longitudinal burning channels. The advantage inherent in such weakened portions is that the sticks will, during the initial phase of the combustion, be shattered transversally across these weakened points by the internal gas pressure, whereafter combustion of this part of the charge will be effected in the same manner as a charge consisting initially of perforated propellant grains of short lengths.
The second alternative, which has longitudinal, continuous or intermittent slits, gives a propellant which normally burns degressively since it also burns along the slits and the burn area, and thus gas production, diminishes continuously. However, the other aspects of the invention allow the degressivity to be compensated for.
As has already been mentioned, another aspect of the present invention relates to the grain, flake-, tube or rod-shaped powder which fills out the remaining portion of the available charge space. This amount of loose powder may, if desired, be compacted around the bundle or bundles of propellant sticks. According to the present invention, the propellant stick bundles suitably consist of 1-, 7-, 19- or 37-hole perforated powder of optimal outer configuration. Other forms and numbers of perforations may also come into consideration.
A propellant charge of the type according to the present invention may be given an extremely high charge density, in that a considerable part of its total volume consists of densely packed tubular propellant sticks. If, moreover, these sticks are exteriorly inhibited by a substance of lower burning speed than the propellant, this part of the charge will obtain a very high progressivity in that the propellant sticks will, at least initially, be burned from the inside with a consequently successively increasing burning area. When the inhibiting substance has been consumed, there will, moreover, be obtained a large stepwise increase in the burning area which makes for further increased gas generation. The previously mentioned weakenings of the propellant sticks are suitably applied at separations of between 10 and 100 times the diameter of the inner burning channels of the tubular propellant. The burning channels of the tubular propellant should preferably be connected with at least every second one of these weakened points.
As a result of the weakened points, there will be obtained a rod-shaped tubular propellant which, in terms of handling and during the ignition phase, will function as a tubular propellant of full length, but which, during burning becomes shattered and is ultimately totally combusted as though it consisted of a normal tubular propellant cut into short lengths. Otherwise, tubular propellant of long lengths shows a marked tendency, after a brief period of combustion, to be shattered by the internal gas pressure into irregular fragments which readily give rise to disastrous pressure peaks in the barrel.
This problem is wholly obviated according to the present invention. One type of weakening which has been established as being particularly advantageous comprises a symmetrically disposed perforation of determined width and completely executed without the removal of any propellant. Thus, such a perforation rather assumes the form of a central incision. Since the perforation leaves a certain amount of propellant on either side, the tubes may retain nevertheless a high degree of cohesion and rigidity. Moreover, in multi-hole propellant, it is often possible to cover, with one single incision, all combustion channels, which ensures a rapid internal overall ignition, effective cracking zones and high charge weight while still imparting superior initial cohesion to the tubes.
As was mentioned above, the weakened propellant sticks will be burnt in the same manner as a corresponding amount of tubular propellant originally cut into shorter pieces, apart from the fact that this burning takes place within an overall smaller volume, since the propellant sticks according to the present invention are, from the outset, concentrated within a smaller volume than would have been the case in loosely disposed, shorter tubular propellant rods.
Another way to prevent the very long propellant sticks from breaking in an uncontrolled manner during combustion is thus to provide every burning channel with a longitudinal slit through to the outside surface, but the propellant will, as already stated, then become degressive.
The primary task of that portion of the charge according to the present invention which consists, from the outset, of loosely disposed, i.e. disorientated flakes, powder grains or short powder rods or tubes lying around the aligned sticks and which may be compacted within reasonable limits is to ensure a rapid total ignition of the entire charge and a rapid initial gas generation. It is also a simple matter to use loose powder to fill out those parts of a throated case which may not be filled, without difficulty, with densely packed bundles of propellant sticks.
The mixture of weakened tubular propellant and one or more types of loosely disposed powder provides moreover considerable opportunities for controlling the combustion process at the desired pressure vs time cycle in the barrel.
The simplest method of filling a case with a propellant charge according to the present invention is based on the procedure of first arranging one or more bundles of long propellant sticks whose total outer diameter generally corresponds to the inner diameter of the throat of the case, or other desired outer dimension, whereafter the bundle, or the bundles, is passed down into the case and the remaining space within the case is filled with loose powder.
It is also conceivable according to the present invention to dispose tubular bundles of propellant sticks such that the loose powder is filled in the middle of the charge. Furthermore, a certain portion, for example the rear half of a cartridge case, may be filled with densely packed weakened tubular propellant sticks and the remainder with powder grains or flakes of any optional type.